Inducing tumor cell death is one of the primary effects of radiotherapy (RT). However, escaping from death, one of the typical characteristics of cancer cells, leads to the resistance of therapy, recurrence, and poor prognosis of cancers. More than 50% of patients with cancer receive RT as part of the clinical management of their disease either with curative intent or in palliative settings in order to contain the symptoms of metastatic diseases, such as pain. RT is often used as a preoperative debulking intervention to facilitate surgical excision, as well as postoperatively to control residual microscopic disease. In all of these applications, RT has been demonstrated to reduce the incidence of local recurrence. From a molecular standpoint, RT causes direct and reactive oxygen species-dependent damage to DNA, potentially culminating in the permanent inactivation of cell division, cellular senescence, or the initiation of cell death programs.

However, more patients treated with RT are still unable to achieve the desired therapeutic effect. Therefore, patients with RT inefficiency should be exposed to the risks of radiation side effects and drug toxicity caused by this therapy. The use of RT urgently needs ancillary drugs to increase the sensitivity of RT, in order to promote RT, achieve the optimal effects, and reduce the damage to normal cells. In addition, more and more evidence has shown the ability of radiation therapy to influence tumor-directed immune responses. Preclinical studies and clinical observations indicated that RT could be a powerful driver to augment the efficacy of immune checkpoint blockade, because of the ability of RT to activate the antitumor immune response and potentially overcome resistance.

The aim of this Special Issue is to highlight the drugs (such as small molecular, natural products and herb medicine), methods and results related to different RTs, or RT multi-modalities, including the chemotherapeutic agents combined with innovative RT techniques to increase tumor responses, pathological response and reduce toxicity, to improve oncological outcomes, to explore the possible biomarkers to predict the outcomes, or micro-environmental factors to influence the patient prognosis. We welcome both original research and review articles.

Potential topics include but are not limited to the following:

• Innovative radiotherapeutic techniques
• Small molecular effects on radiation
• Effects of natural products or herbal medicine on radiotherapy
• Drug repurposing for radiotherapy
• Multi-modality therapy (chemotherapy, immunotherapy, and target therapy combined with radiotherapy)
• Nanoparticle applications for radiotherapy
• Biomarkers for predicting the effects of radiation
• Micro-environmental factors that influence the effects of radiation